Recently, attention has been paid to optical fibers, mainly in communication fields. Particularly in the IT (Information Technology) field, a communication technique that employs the optical fibers is necessary for constructing a high rate Internet network.
The optical fiber has features of (1) low loss, (2) high band, (3) small diameter and light weight, (4) non-induction, (5) resource saving, and the like. A communication system which employs the optical fibers having these features can considerably decrease the number of relays as compared with a communication system which employs conventional metallic cables, can be easily constructed and maintained, and can improve its economical efficiency and reliability.
Further, since the optical fiber can transmit not only light having a single wavelength but also light having a number of different wavelengths simultaneously, a large capacity of a transmission line which can deal with diversified purposes and deal with picture service and the like can be achieved.
Therefore, for the network communication such as the Internet and the like, the employment of optical transmission using optical fibers not only for the communication of a basic network but also for the communication between the basic network and terminal device (a personal computer, a mobile, a game machine and the like) and for the communication between the terminal devices is proposed.
When the optical communication is thus used for the communication between the basic network and the terminal device, an IC which processes information (signals) in the terminal device is operated by an electric signal, and therefore, the terminal device is required to be provided with a unit that converts an optical signal into an electric signal or vice versa such as an optical-to-electric converter or an electric-to-optical converter (herein after, also referred to as “optical/electric converter”) and the like.
For this reason, on the conventional terminal device, a package substrate mounted with an IC chip, and optical elements, such as a light receiving element and a light emitting element and the like which process an optical signal, and parts of the like have been separately mounted, and signals were transmitted and processed by connecting electric wirings and the optical waveguide to these constituent elements.
When the package substrate mounted with an IC chip, the optical elements such as a light receiving element and a light emitting element and the like which processes an optical signal, and parts of the like are mounted separately on such a conventional terminal device, the size of the device itself becomes large, making it difficult to minimize the terminal device.
For this reason, the present inventors have already proposed a substrate for mounting an IC chip in which a conductor circuit and an insulating layer are laminated on both faces a substrate a solder resist layer is formed on an outermost layer, and an optical element is mounted on the substrate, the substrate for mounting an IC chip comprising an optical path for transmitting optical signal, that penetrates therethrough (for example, see Patent Document 1).
On the other hand, a microlens may be used in order to improve photocoupling efficiency between optical parts. As a forming method of the microlens, a method such as techniques of silicon anisotropic etching and photolithography are, utilized has been disclosed (for example, see Patent Documents 2 and 3).
A microlens and a microlens array formed by such a method can be secured onto a package substrate or a printed circuit board by using an adhesive.
Moreover, a method for forming a microlens by using a microjet (inkjet) has been disclosed (for example, see Non-Patent Documents 1 and 2) as a method for forming a microlens in which curing of a resin is performed after directly applying a resin to the substrates.
Patent Document 1: JP-A 2002-329891.
Patent Document 2: JP-A 06-230203
Patent Document 3: JP-A 06-326285
Non-Patent Document 1: D. L. MacFarlane and two others, “Microjet Fabrication of Microlens Arrays”, (IEEE Photonic Technol Lett), United States, 1994, Vol. 6, No. 9, pp. 1112-1114
Non-Patent Document 2: Ishii and three others, “Ink-Jet Fabrication of Polymer Microlens for Optical-I/O Chip Packaging”, (Jpn J Appl Phys Part 1), 2000, Vol. 39, No. 3B, pp. 1490-1493